This invention relates generally to timing circuits and more specifically, it relates to a programmable maintenance timer system for generating an output signal at the expiration of a preselected number of operating hours of industrial equipment. The present invention has particular application in the monitoring of the amount of total operating hours of centrifugal water chilling systems and generating an output signal after a predetermined number of operating hours on the chilling system has elapsed.
In the operation of various types of centrifugal water chilling systems, the number of hours in which any specific system is actually running during the course of a day may vary significantly due to weather conditions, energy conservation systems, and shut-down of the equipment due to certain malfunctions. Thus, the normal service or scheduled maintenance interval has been very difficult to determine within any reasonable degree of accuracy. For example, if a periodic maintenance interval of six months were selected for a given chilling system, this may or may not be frequent enough dependent upon its operating condition. It the case where a chilling system has been subjected to a high level of stress, the maintenance interval for servicing should be required after a lesser number of operating hours.
It would be, therefore, desirable to provide a programmable maintenance timer system which could notify service personnel when servicing is required for each specific installation. The programmable maintenance timer system of the present invention generates an output signal after a specific number of operating hours has elapsed, for instance, 100 hours, 500 hours, or 1,000 hours, etc. to a telemetry system causing a coded message to be transmitted to a monitoring facility. The telemetry system is preferably of the type which is described in the copending patent application Ser. No. 212,299 of A. R. Day III and F. McMenamy entitled "Telemetry System for Centrifugal Water Chilling Systems" and filed on Nov. 14, 1980, and which issued as U.S. Pat. No. 4,387,368 on June 7, 1983.